So in regards to Avengers - Age of Ultron and its placement on the timeline, there's nothing definitive given in the movie itself about its exact placement: no dates seen onscreen or in props from what I could see (I'm going to rewatch it again to double check). No dialogue indicating exactly (or even non-exact) how long its been since the first Avengers movie or Captain America - The Winter Soldier (though both are specifically referenced, the first movie several times throughout and CA-TWS in regards to the fall of SHIELD). Thor does say something to the effect of "at last" in regards to tracking down Loki's Scepter, so they've obviously been looking for it for awhile (pretty much since just before the collapse of SHIELD, per the AoU Prelude comic and dialogue in AoU, though its said they've been looking for it "since the fall of SHIELD" in AoU, but its a difference of days so not a glaring error or anything). Widow also mentions she recruited Banner (in the first movie) "way back when". Seems they're going out of their way not to mention timeline markers in this film.
The closest is towards the end, when Thor mentions the Mind Stone is the fourth Infinity Stone to show up in the "last few years". Since the first one showed up in Captain America - The First Avenger (Tesseract/Space Stone) in 1945, he's obviously referencing it's reappearance when it was taken from SHIELD by Loki (at coincidentally the same time as the Mind Stone showed up on Earth in Loki's Scepter--though I still find it odd that Thanos willingly gave up one of the Stones to Loki, even temporarily). With the Aether (its unknown if its the Soul or Reality stone, but most likely its the Reality Stone) and Orb showing up in the galaxy in 2013 and 2014 respectively (its likely Thor would've known about the events of GotG and Ronan's attack by the time of A-AoU, given Heimdall's ability to see everything), his statement holds true, and at least helps nail down the timeline a tad. A "few" is defined as "not many but more than one". So it can be as little as 2 technically (but is rarely done so since people would just refer to a "couple years"), but is generally used to denote 3-4. Given the real world timeline matches up to the 3 years that likely means, that's a safe bet.
Of course, Cap also mentioned he went in the ice "75 years ago", which is a noticeable overestimation. We know he went into the ice in 1945, which is 70 years before, not 75. Unless we are to assume Age of Ultron occurs in 2020, which is unlikely and doesn't jive with the mentions by Thor of the other Infinity Stones showing up in the past "few years".
The film's internal timeline looks something like this:
Day 1 (Wednesday) (Attack on Strucker's base, Tony and Banner begin working on Ultron that afternoon/evening presumably)
Avengers - Age of Ultron (0:00:00 - 0:20:24)
Day 2 (Thursday) (Tony and Banner work on Ultron, Day 1)
Avengers - Age of Ultron (0:20:25 - 0:20:35)
Day 3 (Friday) (Tony and Banner work on Ultron, Day 2)
Avengers - Age of Ultron (0:20:36 - 0:20:53)
Day 4 (Saturday) (Tony and Banner work on Ultron, Day 3, the party happens that night and Ultron awakens)
Avengers - Age of Ultron (0:20:54 - 0:35:56)
Day 5 (Sunday) (Ultron recruits Wanda and Pietro, Avengers attack Klaue's weapons factory and fight Ultron and the twins, Wanda messes with Hulk's mind leading to Hulk/Hulkbuster (Veronica) fight)
Avengers - Age of Ultron (0:35:57 - 0:58:49)
Day 6 (Monday) (Avengers go to Hawkeye's house to recuperate, Ultron uses the Scepter to mind control Dr. Cho into creating a new body for him, Avengers plan attack on Ultron, Thor and Selvig use the Water of Sight to help figure out what to do, Tony hacks NEXUS to draw Ultron out)
Avengers - Age of Ultron (0:58:50 - 1:17:03)
Day 7 (Tuesday) (Ultron nears completion on uploading his consciousness into the Vision android, Avengers attack and obtain the Vision, Ultron kidnaps Black Widow, Tony, Banner, and Thor bring Vision online, Vision proves his worth by nonchalantly picking up Thor's hammer,)
Avengers - Age of Ultron (1:17:04 - 1:37:11)
Day 8 (Wednesday)* (Avengers final battle with Ultron, Quicksilver sacrifices himself to save Hawkeye and a kid, Vision destroys last Ultron robot)
Avengers - Age of Ultron (1:37:12 - 2:06:13)
Day 9 (Thursday) (Hawkeye returns home)
Avengers - Age of Ultron (2:06:14 - 2:06:44)
At least a few months later** (New Avengers facility is being set up, Tony and Clint have retired, Banner is in hiding, Quicksilver is dead; Cap and Widow begin training the New Avengers team of Falcon, War Machine, Vision, and Scarlet Witch)
Avengers - Age of Ultron (2:06:45 - 2:10:53)
Unknown*** (Thanos steals the Infinity Gauntlet, presumably from an Asgardian vault)
Avengers - Age of Ultron (2:1?:?? - 2:1?:??)
* Tony loads a disk entitled "Friday". This the name of the program (with the female voice), not the day of the week, so its not a continuity screw up. If you look closely to the upper left in the background you'll see a disk entitled "Jocasta" (obvious wink) and another that's partially cut off by the way the shot is framed that reads "??das #1". Maybe Midas? Could be more letters than that, hard to tell. Either way it indicates those names are various programs Tony has written for the Iron Man suits.
** Noted by the birth of Nathaniel Barton, earlier in the movie Barton's wife Laura when she was pregnant, that the baby would be born in a few months (indicating she was likely around 6 months pregnant at that point, when the Avengers were hiding out on Barton's farm). Given Natasha is viewing a photo of baby Nathaniel after he's born, at least 3 months have passed since the final battle with Ultron.
*** It's unknown when the mid-credits scene occurs. Is it during the events of AoU, after, even before? Presumably it occurs afterward, and since it acts as a prelude to Phase 3, placing it after AoU makes sense both chronologically and narratively (unless future evidence indicates otherwise). I also don't have the correct time-code for that in regards to the credits in between the end of the film and the mid credits scene.
As for those time-codes, they're only temporary for the theatrical version, and not much help without firm dates to pin it down. The Extended Edition will obviously be about a half hour longer so when that's eventually released on BluRay at the end of the year, I'll get those posted and split up by chapter).
In terms of AoS: Dr. List is indeed with Strucker at the castle that the Avengers attack at the beginning, and while attempting to delete the various Hydra computer files, he gets zapped by Tony/Iron Man (not sure if it was a stun shot or lethal, and while it may have been a grazing shot of the latter variety, there were no indicators as to whether he was dead or alive).
Therefore, if he appears in any AoS episodes from next week's episode (not this week's, necessarily), we know the AoS season ends before AoU--but that may be unlikely, we'll know for sure in the next couple weeks with the AoS Season 2 finale, and hopefully next week assuming they're doing direct tie-ins to AoU.
